Shock resistant semiconductor microphone having magnetically operatedoverload mechanism

ABSTRACT

AN ELECTROACOUSTIC TRANSDUCER OF THE STRESSED SEMICONDUCTOR TYPE WHEREIN THE STRESSING MEMBER OR SEMICONDUCTOR IS MOUNTED ON A FIRST MEMBER WHICH IS MAGNETICALLY COUPLED WITH A SELECTED BREADAWAY FORCE TO A FIXED MOUNTING MEMBER. OVERLOAD STRESS OVERCOMES THE MAGNETIC COUPLING THEREBY PERMITTING THE STRESSING MEMBER AND SEMICONDUCTOR ELEMENT TO SEPARATE AND THUS PREVENT MECHANICAL DAMAGE TO THE TRANSDUCER.

Jm. 30, 1973 D. F. HIESTAND SHOCK RESISTANT SEMICONDUCTOR "MICROPHONEHAVING MAGNETICALLY OPERATED OVERLOAD MECHANISM Filed July 26, 1971 FIG/INVENTOR DAVID F. HIESTAND M iv! ATTORNEY United States Patent 3,714,376SHOCK RESISTANT SEMICONDUCTOR MICRO- PHONE HAVING MAGNETICALLY OPERATEDOVERLOAD MECHANISM David F. Hiestand, Lombard, Ill., assignor to GTEAutomatic Electric Laboratories Incorporated, Northlake, Ill.

Filed July 26, 1971, Ser. No. 166,175 Int. Cl. H04r 23/00 US. Cl.179-110 B 2 Claims ABSTRACT OF THE DISCLOSURE An electroacoustictransducer of the stressed semicon ductor type wherein the stressingmember or semiconductor is mounted on a first member which ismagnetically coupled with a selected breakaway force to a fixed mountingmember. Overload stress overcomes the magnetic coupling therebypermitting the stressing member and semiconductor element to separateand thus prevent mechanical damage to the transducer.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates generally to the field of electroacoustic transducers and moreparticularly to a stressed semiconductor microphone having a magneticstress overload protection means.

Description of the prior art The advantages of semiconductor elements aselectroacoustic transducers have been recognized for many years. In thetypical arrangement a PN junction and a stressing member are mounted inmechanical contact with one another such that acoustic energy varies thestress on the junction and converts the acoustic energy to electricalenergy. Generally the semiconductor junction is disposed on a fixedmounting and the stressing member is affixed to a microphone diaphragm,however, the reverse arrangement is also known. The problem whichattends the use of the stressed semiconductor microphone has been thefragility of the semiconductor elements which leaves the microphonesensitive to mechanical damage when subjected to rough handling as inthe common telephone handset.

Prior to the present invention the shock damage susceptibility of thestressed semiconductor microphone was recognized and attempts were madeto alleviate this problem. One such shock-resistant microphone isdescribed in US. Patent No. 3,440,363 which issued to H. J. Boll on Apr.22, 1969. That patent describes a semiconductor microphone of thecantilever type wherein the semiconductor is mounted in a bar member andis indirectly stressed through application of deflection forces to oneend of the bar member. The bar member has a double fulcrum and isretained against the fulcrum pivot points by a spring member such thaton the application of shock overloads the bar member mechanically pivotsat the spring end rather than bending excessively. While the overloadprotection provided by the apparatus disclosed in the referenced patentmay be satisfactory in certain applications it is of a fixed ornon-adjustable nature, i.e. the spring force and thus the overload levelnecessary to call the protective feature into play may not be ad justedto meet varying environmental or handling condi* tions.

OBJECTS AND SUMMARY OF THE INVENTION From the foregoing it will beunderstood that among the various objectives of the present inventionare included:

The provision of a new and novel shock-resistant semiconductormicrophone;

The provision of apparatus of the above-described character wherein thelevel of shock overload protection may be adjusted; and

The provision of apparatus of the above-described character whereinshock overload protection is provided by a variable magnetic couplingbetween the semiconductor and stressing member of the microphone.

These and other objectives of the present invention are eflicientlyachieved by mounting either the semiconductor element or the stressingmember on a movable member which is magnetically coupled with anadjustable breakaway force to a supporting member. On the application ofan overload stress to the microphone the magnetic attraction is overcomeand the movable member is permitted to move away from its supportingmember thus separating the semiconductor element from the stressingmember and precluding physical damage to the semi conductor element.

The foregoing as well as other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration ofa first embodiment of a shock-resistant semiconductor microphoneconstructed in accordance with the principles of the present invention;

FIG. 2 is a schematic cross-sectional view of an alternative embodimentof the present invention;

FIGS. 2A and 2B schematically illustrate a top view of the magneticelements of the embodiment of FIG. 2; and

FIG. 2C is a schematic top view of the base member of the embodiment ofFIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENTS Turning now to FIG. 1 there isillustrated a shockresistant semiconductor microphone in accordance withthe present invention. A stress-sensitive semiconductor element 10 ismounted on a member 12 which is movable in rotation about a pivot point14 and mounted on a post 16 aflixed to the microphone outer case 18. Astressing member 20 is afiixed to any suitable means for convertingacoustic to mechanical energy such as the diaphragm 22 illustrated. Asupporting member 24 is disposed above the movable'member 12 and has afirst permanent magnet 26 fixed thereto. The movable member 12 isprovided with a second permanent magnet 28 disposed with its polarityreversed with respect to magnet 26. The first magnet 26 is axiallymovable with respect to the second magnet 28 by means of an adjustmentscrew 30 threaded through the outer case 18. In this fashion themagnetic attraction between magnets 26 and 28 may be varied such thatthe level of overload stress necessary to overcome the mag neticcoupling may be selected in accordance with the handling to which themicrophone may be subjected. When an overload stress above the selectedlevel is placed on the microphone the magnetic coupling is overcome andthe movable member 12 rotates downward about the pivot point 14 thuscarrying the semiconductor element 10 out of contact with the stressingmember 20. Thus the semiconductor element is efiiciently protected fromdamage by stress overloads.

With reference now to FIGS 2 through 2C there are schematicallyillustrated several views of an alternative embodiment of the presentinvention. In this embodiment first and second magnets, 32 and 34 aredisposed in a correspondingly shaped outer case 36. Magnet 32 is shapedat its circumference to mate with and be longitudinally fixed withrespect to the case 36 but free to rotate about the longitudinal axis oithe microphone. The second magnet 34 is basically disc shaped but has aperipheral notch or notches 38 formed therein which are adapted to matewith correspondingly shaped members 40 disposed on the interior of themicrophone case 36. Thus the second magnet 34 is longitudinally movablewithin the case 36 but is constrained in rotation. The second magnet 34is provided with a centrally disposed post 42 which is adapted to passthrough a central aperture 44 in the first magnet 32. The top of thepost 42 is provided with a mounting plate 46 upon which a stresssensitive semiconductor element 48 may be disposed. A stressing member50 carried by a suitable acoustic-to-mechanical energy conversion means(not shown) contacts the semiconductor element 48 in the usual mannersince the magnetic attraction between magnets 32 and 34 tend to maintainthis relationship. The degree of magnetic attraction is easily adjustedthrough rotation of magnet 32 with respect to rotationally constrainedmagnet 34 to any selected level. When a stress overload in excess of theselected level is applied to the microphone of FIG. 2 the magneticattraction between magnets 32 and 34 is overcome and magnet 34 bearingthe semiconductor element 48 moves axially downward thereby precludingshock induced damage.

It will thus be seen that the applicant has provided an improvedshock-resistant semiconductor microphone wherein the objectives setforth hereinabove are efiiciently achieved. Since certain changes in theabovedescribed contruction will occur to those skilled in the artwithout departure from the scope of the invention it is intended thatall matter contained in the foregoing description or shown in thevarious views of the appended drawing shall be interpreted asillustrative and not in a limiting sense.

Having described what is new and novel and desired to secure by LettersPatent, what is claimed is:

1. An improved stressed-semiconductor microphone comprising a microphonehousing,

a first magnetic member axially fixed with respect to said housing, andhaving an axial aperture disposed therein,

a second magnetic member axially movable with respect to said housing,

a mounting member disposed on said second magnetic member, in axialalignment with and extending through said aperture in said firstmagnetic member,

a stress-sensitive semiconductor element disposed on said mountingmember,

means for applying a variable stress to said semiconductor element inresponse to the impingement of acoustic energy on said microphone,

the magnetic attraction between said first and second magnetic membersbeing preselected to maintain said semiconductor element in contact withsaid stress applying means with a preselected breakaway force such thatthe application of overload stress to said micro-phone in excess of saidpreselected breakaway force overcome said magnetic attraction and movessaid semiconductor element away from said stress applying means.

2. Apparatus as recited in claim 1 wherein said first magnetic member isrotatably movable with respect to said housing, and

said second magnetic member is fixed in rotation with respect to saidhousing,

whereby the magnetic attraction between said first and second magneticmembers is adjustable through rotation of said first magnetic member.

References Cited UNITED STATES PATENTS 3,440,363 4/1969 B011 317-235 M3,404,243 10/1968 Krieger et a1. 179-110 B KATHLEEN H. CLAFFY, PrimaryExaminer T. L. KUNDERT, Assistant Examiner US. Cl. X.R.

